When I decided to go to university I didn't know what I wanted to do. When I had an opportunity to take an elective I took Drama by chance, even though I'd never taken a Drama course or even been in a play in high school. Two years later I was majoring in Drama and I knew I wanted to be an actor.
The brain seems to be made up of a bewildering complexity of parts, and the cells within the parts seem to be characterized by an inscrutable complexity of form, extent, and relationships with each other.